1. Field of the Invention
The present invention pertains to an optical writing device that writes or displays images on an image receiving surface, e.g., a photosensitive material, a screen, or a naked eye, and more particularly, to an optical writing device in which an electro-optical material such as PLZT is used for the light shutter elements.
2. Description of Related Art
An image forming apparatus that forms images (latent images) by exposing photographic paper or film using a silver photosensitive material or a photosensitive drum for electronic photography by means of an optical writing device is conventionally known. One solid-state scanning type form of this optical writing device, in which a PLZT optical shutter element array is used, is known. In an optical writing device of this solid-state scanning type, a polarizer and an analyzer are located in the upstream side and the downstream side of the light path relative to the light shutter element array, respectively. The polarizer and the analyzer are arranged in a Cross-Nicoled fashion relative to the light shutter elements. Because PLZT is a material that has an electro-optical effect, as is publicly known, light may be allowed to pass through or prevented from passing through each light shutter element by controlling the applied voltage. FIG. 6 shows the relationship between the drive voltage for each light shutter element and the amount of pass-through light. In the drawing, the characteristic A represents the characteristic in the initial stage, and the light shutter element is driven at all times using a half-wavelength voltage V.sub.H that achieves the maximum amount of pass-through light.
However, when an electrical field running in a certain direction is applied to the light shutter element at all times, the initial characteristic A changes into the characteristic B. If the application of the electric field is continued, the characteristic changes into the characteristic C. In other words, even if the same voltage H.sub.V is applied, the amount of pass-through light decreases by .DELTA.I.sub.B for the characteristic B and by .DELTA.I.sub.C for the characteristic C. This change in the amount of pass-through light is larger for elements that are driven more frequently per unit of time, which leads to the problem of degraded image quality.
Therefore, the applicant has proposed, as disclosed in Laid-Open Japanese Patent Application HEI 4-115219, to incorporate a means to monitor the characteristic of the light shutter elements and control the recovery of the characteristic in accordance with the monitored amount of light. However, using this invention, because the attempt to recover the characteristic is made during the application of an alternating electrical field, a relatively long period of time is required, and due to the need to monitor the amount of light corresponding to the alternating electrical field, the circuit becomes complex in construction.